1. Field of the Invention
The invention relates to an optoelectronic transmit module including at least one transmit element, at least one monitor element and a coupling device having at least one optical coupling element and at least one reflective element, both the reflective element and the coupling element of the coupling device being disposed opposite a radiation-sensitive surface of the monitor element and a section of an active surface of the transmit element, the section being located on only one component side of the transmit element.
Optoelectronic transmit modules with active components, in particular semiconductor lasers, frequently have a feedback circuit for regulating a temperature-dependent and aging-dependent driver current for the semiconductor laser. A part of the radiation emitted by the laser is detected by a photodiode which is used as a monitor diode. A diode current is available as a regulating signal for the feedback circuit. Fluctuations in the intensity of the emitted radiation can thus be compensated.
A transmit module for semiconductor lasers is described in Published UK Patent Application GB 2 276 493 A, corresponding to U.S. Pat. No. 5,500,869. A monitor diode, a semiconductor laser and a lens system are disposed in series on a silicon carrier. Optical axes of the three modules are aligned coaxially with respect to one another and run parallel to the surface of the silicon carrier. The semiconductor laser has two emission directions. On one hand, a main emission direction faces the lens system. On the other hand, a smaller part is emitted in an opposed direction and is detected by the monitor diode in order to regulate the driver current. The previously known optical transmit module requires two emission directions and a precise adjustment of the individual modules with respect to one another.
An optical transmit module of the type mentioned at the outset above can be found in U.S. Pat. No. 4,733,094. The known transmit module is accommodated in a transistor housing and has, inter alia, a support plate which rests on a base component of the transistor housing. On the support plate there is a base plate on which a transmit element in the form of a luminescent diode and a photodiode are disposed one next to the other. Above the transmit element in the direction of radiation there is a semitransparent mirror after which, in the direction of radiation, a coupling element in the form of a microlens is disposed. The microlens is held in the upper part of a pot-like cover of the transistor housing. A part of the light which is output by the transmit element is reflected by the semitransparent mirror to a further mirror and directed by the latter onto the photodiode.